Coupling an electric machine and fluid-end

ABSTRACT

A submersible fluid system for operating submerged in a body of water includes a fluid-end that has a fluid rotor disposed in a fluid-end housing. An electric machine housing is coupled to the fluid-end housing and includes a hermetically sealed cavity. An electric machine, such as a motor and/or generator, is disposed entirely within the cavity of the electric machine housing. The electric machine includes an electric machine stator and an electric machine rotor. A magnetic coupling couples the electric machine rotor and the fluid rotor.

CLAIM OF PRIORITY

This application is a U.S. National Stage of PCT/US2012/054843 filed onSep. 12, 2012.

BACKGROUND

Operation of fluid systems such as pumps, compressors, mixers,separators and other such systems submerged underwater is difficultbecause the operating environment is harsh, particularly if thatenvironment is deep seawater. The water surrounding the system and oftenthe process fluid flowing through the system is corrosive. The ambientenvironment can be cold, making many materials brittle and causing largethermal expansion/contraction of equipment as the equipment cyclesbetween hot operating and cold not-operating states. The hydrostaticpressure of the water and/or process fluid can be substantial.Furthermore, installation and access to the fluid systems formaintenance and repair is difficult and expensive because the systemsare often deployed in geographically remote locations and at depthsinaccessible by divers, therefore requiring purpose-built vessels,skilled personnel and robotic equipment.

SUMMARY

The concepts herein encompass a submersible fluid system for operatingsubmerged in a body of water. The submersible fluid system includes afluid-end that has a fluid rotor disposed in a fluid-end housing. Anelectric machine housing is coupled to the fluid-end housing andincludes a hermetically sealed cavity. An electric machine, such as amotor and/or generator, is disposed entirely within the cavity of theelectric machine housing. The electric machine includes an electricmachine stator and an electric machine rotor. A magnetic couplingcouples the electric machine rotor and the fluid rotor.

The concepts herein encompass a method of coupling an electric machineto a fluid-end of a submersible fluid system. According to the method, arotor of the electric machine is maintained in an area of a firstpressure that is hermetically sealed from a fluid rotor of thefluid-end. The fluid rotor of the fluid-end resides in an area of asecond, different pressure. The rotor of the electric machine is coupledto the fluid rotor with a (touchless) magnetic coupling through astationary wall between the rotor of the electric machine and the fluidrotor. The (touchless) magnetic coupling causes the fluid rotor to movewith the rotor of the electric machine or vice versa.

The concepts herein encompass a submersible fluid-end. The has a shaftcontained in a submersible fluid-end housing. The shaft has a permanentmagnet. The has a rotor extending into the electric machine. The motorhas a rotor permanent magnet and the rotor resides in a hermeticallysealed cavity defined by an electric machine housing. The permanentmagnet resides proximate the rotor permanent magnet communicatingmagnetic flux between the permanent magnet and the pump permanent magnetto couple the shaft with the rotor shaft.

The concepts above can encompass some, none or all of the followingfeatures.

In certain instances, an end of the fluid rotor can extend into aninterior bore of the electric machine rotor and a magnet is coupled toan exterior of the end of the fluid rotor. Another magnet is coupled tothe electric machine rotor, and resides in the interior bore theelectric machine rotor. A wall is provided between the magnets. Incertain instances, the wall includes a substantially non-magneticallyconductive cylinder. In certain instances, a support can be providedthat extends from an end of the electric machine housing towards thefluid-end housing that clamps the cylinder between the support and thefluid-end housing. The support can be springingly biased towards thefluid-end housing. In certain instances, a fluid passage can be providedthrough the support and into an interior of the cylinder. The fluidpassage can be coupled to receive fluid from an exterior of the fluidsystem and communicate the fluid to an interior of the cylinder. Incertain instances, that fluid can be substantially gas. In certaininstances, the cylinder can be an inner sleeve made of gas impermeableceramic or glass within a fiber-matrix composite outer sleeve. Incertain instances, the outer sleeve can compressively strain the innersleeve. In certain instances, the sleeve can include a seal surfaceabout one end and a seal surface about an opposing end.

In certain instances, the sealed cavity of the electric machine housingcan contain gas at a pressure of about one atmosphere, and an interiorof the cylinder can contain a fluid at a pressure of about the pressureof the fluid entering the fluid rotor at the fluid-end. In certaininstances the seals sealing the cavity from the fluid-end housing areentirely static seals. In certain instances, the electric machineincludes a magnetic bearing supporting the electric machine rotor torotate within the electric machine stator. The magnetic bearing can bewholly contained within the sealed cavity. In certain instances thefluid-end can contain a fluid-film type bearing supporting the fluidrotor. In certain instances, the electric machine rotor includes apermanent magnet that interacts with the stator of the electric machineto rotate the electric machine rotor relative to the stator and/or togenerate electricity when rotated relative to the stator. In certaininstances the electric machine is a motor and the fluid rotor is a pumprotor.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an example fluid system.

FIG. 2A is a side cross-sectional view of an example integrated electricmachine and fluid-end that can be used in the example fluid system ofFIG. 1.

FIG. 2B is a side cross-sectional view of a fluid inlet portion and themagnetic coupling between an electric machine rotor and a fluid-endrotor in the example fluid system of FIG. 2A.

FIG. 2C is a side cross-sectional view of a fluid outlet portion andsump of the example fluid-end of FIG. 2A.

FIG. 3 is a flow schematic of the example fluid system of FIG. 1.

DETAILED DESCRIPTION

Fluid systems of the type disclosed herein act on fluids (“processfluids”) that may comprise substantially single phases, e.g. water, oilor gas, or a mixture of more than one phase (“multiphase”) that mayinclude two or more phases and often entrained solids, e.g. sand, metalparticles and/or rust flakes, wax and/or scale agglomerations, etc. FIG.1 is a side view of an example fluid system. FIG. 1 depicts an examplefluid system 100 constructed in accordance with the concepts describedherein. The fluid system 100 includes a fluid-end 102 coupled to anelectric machine 104. In certain instances, the fluid system 100 mayalso include a fluid separator system 108.

Fluid system 100 may be operated submerged in open water e.g. outside ofa hydrocarbon production or injection well in a lake, river, ocean orother body of water. To this end, fluid-end 102 and electric machine 104are packaged within a pressure vessel sealed to prevent passage of fluidbetween the interior of the pressure vessel and the surroundingenvironment (e.g. surrounding water). Fluid system 100 components areconstructed to withstand ambient pressure about fluid system 100 andthermal loads exerted by the surrounding environment, as well aspressures and thermal loads incurred in operating electric machine 104and fluid-end 102.

In certain instances, e.g. subsea applications, fluid-end 102, electricmachine 104 and fluid separator system 108 may be carried on a skid 110or other structure of fluid system 100 that aligns with, and engagesother subsea structures, e.g. by way of guide tubes 112 that captureguide posts of a corresponding subsea structure, or through interactionof a large cone-to-cone-plus-pin-and-cam arrangement (not shown butfamiliar to those skilled in the art of guidelineless subsea systems).When the fluid system is referred to as a “subsea” fluid system, it isnot to say that the fluid system is designed to operate only under thesea. Rather, the subsea fluid system is of a type that is designed tooperate under the rigors encountered at or near the bottom of an openbody of water, such as an ocean, a lake, a river or other body of saltor fresh water. An auxiliary source of liquids 114 can be interfaced toskid 110 to provide liquids to the system, e.g. corrosion, scale andhydrate inhibiting chemicals.

One or more dampers 120 may be affixed external to the fluid system 100to damp impact of the fluid system 100 with surfaces, such as on asubsea structure or a transportation vessel deck. The dampers 120 may beconfigured to maintain a level orientation of the fluid system 100 insituations where the surface is not level. The dampers 120 may be fluiddampers or other types of shock or impact absorbing devices.

As described in more detail below, electric machine 104 is analternating current (AC), synchronous, permanent magnet (PM) electricmachine having a rotor that includes permanent magnets and a stator thatincludes a plurality of formed or cable windings and a (typically)stacked-laminations core. In other instances electric machine 104 can beanother type of electric machine such as an AC, asynchronous, inductionmachine where both the rotor and the stator include windings andlaminations, or even another type of electric machine. Electric machine104 can operate as a motor producing mechanical movement fromelectricity, a generator producing electric power from mechanicalmovement, or alternate between generating electric power and motoring.In motoring, the mechanical movement output from electric machine 104can drive fluid-end 102. In generating, fluid-end 102 suppliesmechanical movement to electric machine 104, and electric machine 104converts the mechanical movement into electric power.

In instances where fluid-end 102 is driven by electric machine 104,fluid-end 102 can include any of a variety of different devices. Forexample, fluid-end 102 can include one or more rotating and/orreciprocating pumps, rotating and/or reciprocating compressors, mixingdevices, or other devices. Some examples of pumps include centrifugal,axial, rotary vane, gear, screw, lobe, progressing cavity,reciprocating, plunger, diaphragm and/or other types of pumps. Someexamples of compressors include centrifugal, axial, rotary vane, screw,reciprocating and/or other types of compressors, including that class ofcompressors sometimes referred to as “wet gas compressors” that canaccommodate a higher liquid content in the gas stream than is typicalfor conventional compressors. In other instances fluid-end 102 mayinclude one or more of a fluid motor operable to convert fluid flow intomechanical energy, a gas turbine system operable to combust an air/fuelmixture and convert the energy from combustion into mechanical energy,an internal combustion engine, and/or other type of prime mover. In anyinstance, fluid-end 102 can be single or multi-stage device.

While FIG. 1 illustrates a vertically-oriented electric machine 104coupled to a vertically-oriented fluid-end 102, other implementationsmay provide for a horizontally-oriented electric machine coupled to ahorizontally-oriented fluid-end, a vertically-oriented electric machine104 coupled to a horizontally-oriented fluid-end 102, ahorizontally-oriented electric machine 104 coupled to avertically-oriented fluid-end 102, as well as still other orientationsof electric machine 104 and fluid-end 102, including non-in-line andnon-perpendicular arrangements.

Although shown with a single fluid-end 102, electric machine 104 canalso be coupled to two or more fluid-ends 102 (to drive and/or be drivenby the fluid-ends 102). In certain instances, one or more fluid-ends 102can be provided at each end of electric machine 104, and in anyorientation relative to electric machine 104. For example, in aconfiguration with two fluid-ends 102, one may be provided at one end ofelectric machine 104 and another provided at an opposing end of electricmachine 104, and the fluid-ends 102 may be oriented at different anglesrelative to electric machine 104. In another example, a configurationwith two fluid-ends 102 can have one provided at one end of electricmachine 104 and another coupled to the first fluid-end 102. Also, ifmultiple fluid-ends 102 are provided, they need not all be of the sametype of device and they need not operate on the same fluid, i.e., theycould operate on different fluids.

FIG. 2A is a side cross-sectional view of an example electric machine202 and fluid-end 204 that can be used in the example fluid system 100of FIG. 1. Fluid-end 204 includes a fluid rotor 206 disposed in afluid-end housing 208. Fluid-end housing 208 contains process fluidsflowing from an inlet 250 near electric machine 202 to an outlet 272distal the electric machine. Electric machine 202 is carried by, andcontained within, an electric machine housing 210 attached to fluid-endhousing 208 of fluid-end 204 by way of end-bell 214 a. Electric machinehousing 210 is attached at its upper end to end-bell 214 b, which isattached to cap 233. The aforementioned attachments are sealed to createa pressure vessel encapsulating electric machine 202 that preventspassage of fluid between its interior and the surrounding environment(e.g. water). Another collection of parts and interfaces (describedlater in this disclosure) prevents passage of fluid between electricmachine 202 and fluid-end 204. As a result of the mentioned barriers,electric machine 202 operates in its own fluid environment, which may begas or liquid depending on specific trade-offs (with gas preferred froma system overall efficiency perspective). FIG. 2A depicts aclose-coupled submersed fluid system 200 in that electric machine 202structural elements attach directly to fluid-end 204 structuralelements.

Electric machine 202 disposed within electric machine housing 210includes an electric machine stator 218 and an electric machine rotor220. Electric machine housing 210 is coupled to the fluid-end housing208 and includes a hermetically sealed cavity. The cavity has a gas at apressure less than the hydrostatic pressure at the specified underwaterdepth. The electric machine 202 is disposed within the cavity of theelectric machine housing. Electric machine stator 218 is interfaced withan external power supply by penetrators/connectors 238 whichpass-through lower end-bell 214 a. It is known to those skilled in theart of underwater electric power interconnect systems that minimizingpressure differential acting across such interfaces is recommended forlong-term success. Electric machine rotor 220 is magnetically-coupled torotate with process fluid rotor 206 with a magnetic coupling 258. Inother instances, a mechanical coupling could be used. Electric machinerotor 220, which can be tubular, includes a rotor shaft (or core in thecase of an AC machine) 221 and permanent magnets 226 affixed to theexterior of rotor shaft 221, particularly, in an area proximate statorcore 222. The magnetic coupling 258 couples the electric machine rotor220 and the fluid rotor 206 to rotate at the same speed and withoutcontact (i.e., out-of-contact magnetic coupling). The fluid rotor 206 isdisposed to rotate in the fluid-end housing 208 and to receive andinteract with a process fluid flowing from the inlet 250 to the outlet272 of the fluid-end housing 208. The fluid rotor 206 is configured tothrust upwards toward the upper end when rotating.

Permanent magnets 226 are secured to rotor shaft 221 by a sleeve 228including any material and/or material construct that does not adverselyaffect the magnetic field and that satisfies all other design andfunctional requirements. In certain instances sleeve 228 can be madefrom an appropriate non-ferrous metal, e.g. American Iron and SteelInstitute (AISI) 316 stainless steel or a nickel chromium alloy, e.g.Inconel (a product of Inco Alloys, Inc.), or it can include a compositeconstruct of high strength fibers such as carbon-fiber, ceramic fiber,basalt fiber, aramid fiber, glass fiber, and/or another fiber in e.g. athermoplastic or thermoset matrix. Permanent magnets 226 provide amagnetic field that interacts with a magnetic field of stator 218 to atleast one of rotate electric machine rotor 220 relative to stator 218 inresponse to electric power supplied to stator 218, or to generateelectricity in stator 218 when rotor 220 is moved relative to stator218.

Electric machine rotor 220 is supported to rotate in stator 218 bymagnetic bearings 230 a and 230 b separated a significant distancerelative to the length of electric machine rotor 220, and typically, butnot essentially, proximate the ends of electric machine rotor 220. In atleast one alternative to the configuration shown in FIG.2A, magneticbearing 230 a might be positioned closer to stator core 222 such that asubstantial portion or even all of magnetic coupling 258 extends beyondmagnetic bearing 230 a in what is known to those skilled in the art ofrotating machinery as an over-hung configuration. Magnetic bearing 230 ais a combination (“combo”) magnetic bearing that supports electricmachine rotor 220 both axially and radially, and magnetic bearing 230 bis a radial magnetic bearing. In the case of a vertically-orientedelectric machine 202, a passive magnetic lifting device 254 may beprovided to carry a significant portion of the weight of electricmachine rotor 220 to reduce the capacity required for the axial portionof magnetic combo bearing 230 a, enabling smaller size and improveddynamic performance for combo bearing 230 a. Machines incorporatingmagnetic bearings typically also include back-up bearings 231 a and 231b to constrain motor rotor 220 while it spins to a stop in the event themagnetic bearings cease to be effective, e.g. due to loss of power orother failure. Back-up bearings 231 a, 231 b will support motor rotor220 whenever magnetic bearings 230 a, 230 b are not energized, e.g.during transportation of fluid system 100. The number, type and/orplacement of bearings in electric machine 202 and fluid-end 204 may bedifferent for different fluid system 100 configurations.

Other elements of electric machine 202 are intimately associated withintegrated fluid-end 204, and an overview of a few higher-levelattributes for submersed fluid system 200 at this juncture mayfacilitate reader understanding of the functions and integratedoperating nature of those other electric machine 202 elements.

Certain embodiments of subsea fluid system 200 may include: An electricmachine 202 the contents of which operate in a gas environment atnominally 1-atmosphere pressure delivering lower losses than existingtechnologies (e.g. while its electric machine housing 210 is exposedexternally to potentially deep water and associated high pressure); anelectric machine 202 that utilizes magnetic bearings 230 a, 230 b foradditional loss savings compared to machines operating in a submergedliquid environment using e.g. rolling element or fluid-film bearings; amagnetic coupling 258 for which an inner portion 262 is contained inpotentially very high pressure process fluid and is isolated from itsassociated outer portion 293 located inside the nominally 1-atmospherepressure environment of electric machine 202 by a static (non-rotating)sleeve 235 that along with its associated static (non-rotating)end-seals 246, 248 is able to withstand the large differential pressureacting there-across; an electric machine 202 that because of its1-atmosphere operating environment, use of magnetic bearings 230 a, 230b, and use of a magnetic coupling(s) 258 to engage its integratedfluid-end(s) 204, produces much less heat during operation compared toother known technologies (used in submersed fluid system 200applications) and that therefore can transfer its heat to thesurrounding environment using passive, durable and low-cost materialsand techniques (including no circulated coolant and associatedpump-impeller, etc.); a manner of cooling the magnetic coupling 258 thatin certain circumstances may allow the process fluids-submerged portionof that coupling to spin inside a gas-core (with accordant lower lossand other benefits); one or more fluid-ends 204 that employ fluid-filmbearings 264 a, 264 b, 274 or any other types of bearings lubricated andcooled by process fluid (e.g., water or oil or a combination thereof) oralternative fluid; one or more fluids-ends 204 that employ bearings 264a, 264 b, 274, provided as fluid-film bearings, magnetic bearings or anyother types of bearings at those same or different locations, or acombination of any types of bearings; an upper-inlet/lower outletvertical fluid-end 204 arrangement that provides a sump 271 at itslower-end to secure fluid-film bearings 264 b, 274 in a serviceableenvironment.

While the contents of electric machine 202 was previously described asoperating in a nominally 1-atmosphere pressure environment, the fluidsystem 200 could alternately be configured to maintain the contents ofelectric machine 202 in an environment compensated to be substantiallyequal to the pressure of the water around fluid system 200.

While the magnetic coupling 258 was previously described with the innerportion 262 in the process fluid and the outer portion 293 in thenominally 1-atmosphere pressure environment of electric machine 202, asan alternative, the magnetic coupling 258 could be provided with theopposite topology, having an inner portion in the nominally 1-atmospherepressure environment and an outer portion in the process fluid.

Electric machine housing 210 (and associated parts) plus magneticcoupling 258 combined with sleeve 235 (and associated parts) establishthree substantially separate environments that can be exploited forunprecedented value for submersed fluid systems 200, i.e.: A potentiallyprocess-gas-environment inside sleeve 235 at the upper end of fluid-end204 (otherwise process multiphase fluid or liquid); a nominally1-atmosphere gas environment outside sleeve 235 and inside electricmachine housing 210; an underwater environment outside of electricmachine housing 210 (and also outside fluid-end housing 208). In analternative embodiment, the environment inside electric machine housing210 may be pressurized (e.g. with gas or liquid) a little or a lot (i.e.any of various levels up to and including that of the process fluid),with accordant tradeoffs in overall system efficiency (increasedlosses), possibly different cross-section for e.g. electric machinehousing 210, upper sleeve 296 and lower sleeve 298, reducedcross-section of sleeve 235 and therefore increased efficiency ofmagnetic coupling 258, different pressure field across e.g. electricpower penetrators, different heat management considerations, etc. Withthe preceding context, additional description will now be provided forelectric machine 202 components and other subsea fluid system 200components.

Consistent with the present disclosure, it is to be understood thatprocess fluid may be used to lubricate and cool fluid-film or othertypes of bearings 264 a, 264 b, 274 in fluid-end 204, and to coolmagnetic coupling 258. It is further understood that process fluid inliquid form will better satisfy the requirements ofprocess-lubricated-and-cooled bearings (not applicable if fluid-end 204uses magnetic bearings), and that process fluid containing at least somegas may benefit the coupling-cooling application, i.e. by reducingdrag-loss associated with process fluid rotor 206 motion and conductingheat from inside sleeve 235. Process fluid for the noted applicationsmay be sourced from any of, or more than one of, several locationsrelative to submersed fluid system 200 depending on the properties ofthe process fluid at such source location(s) (e.g. water, oil, gas,multiphase), the pressure of such source(s) relative to the point ofuse, and the properties required for fluid at the point of use. Forexample, process fluid may come from upstream of submersed fluid system200, such as from buffer tank 278, liquid reservoir 284 or other sourcesincluding some not associated with the process stream passing throughsubmersed fluid system 200 and/or some associated with the processstream passing through submersed fluid system 200 that are subject toe.g., pre-conditioning before joining the process stream passing thoughsubmersed fluid system 200 (e.g. a well stream that is choked-down to alower pressure before being co-mingled with one or more lower pressureflow streams including the flow stream ultimately entering submersedfluid system 200). Process fluid may be sourced from within submersedfluid system 200 itself (e.g. from any of submersed fluid system 200pressure-increasing stages, proximate outlet 272, from sump 271 and/orimmediately adjacent the respective desired point of use). Process fluidmay be sourced downstream of submersed fluid system 200, e.g. from thedownstream process flow stream directly or from liquid extraction unit287, among others. Non-process-stream fluids may also be used forlubrication and cooling, such as chemicals available at the seabedlocation (which is normally injected into the process stream to inhibitcorrosion and/or the formation of e.g. hydrates and/or deposition ofasphaltenes, scales, etc).

In instances where the upstream process fluid is used for lubricationand/or cooling, and the source does not exist at a pressure greater thanthat at the intended point of use, such process fluid may need to be“boosted.” That is, the pressure of such process fluid may be increasedusing e.g. a dedicated/separate ancillary pump, an impeller integratedwith a rotating element inside subsea fluid system 200, or by some othermeans. In certain implementations the pressure drop across the fluid-endinlet homogenizer (i.e. mixer) 249 can create a pressure bias sufficientto deliver desired fluids from upstream thereof to e.g. upper radialbearing 264 a and coupling chamber 244, the latter being the spacesurrounding magnetic coupling inner portion 262 and residing insidesleeve 235 (this implementation is discussed further herein).

Regardless the process fluid source, it may be refined and/or cleanedprior to being delivered to the point(s) of use. For example, multiphasefluid may be separated into gas, one or more liquid streams, and solids(e.g. sand, metal particles, etc.), with solids typically diverted toflow into fluid-end 204 via its main inlet 250 and/or collected fordisposal. Such fluid separation may be achieved using e.g.gravitational, cyclonic centrifugal and/or magnetic means (among othermechanisms) to achieve fluid properties desired for each point of use.After the fluid has been cleaned, it may also be cooled by passing therefined fluid through e.g. thin-walled pipes and/or thin platesseparating small channels, etc. (i.e. heat exchangers) exposed to thewater surrounding fluid system 200.

Electric machine 202 includes a cap 233 secured to upper end-bell 214 b.For the configuration shown in FIG. 2A, stub 234 is pressed downwardonto sleeve 235 by spring mechanism 239 reacting between shoulderbearing ring 240 and shoulder bearing ring 289. End-bell 214 b, electricmachine housing 210, end-bell 214 a, fluid-end housing 208, sleevesupport ring 270, and various fasteners associated with the precedingitems close the axial load path for stub 234 and sleeve 235. Stub 234contains an internal axial conduit 242 connecting the processenvironment inside sleeve 235 with a cavity provided between the upperend of stub 234 and the underside of cap 233. Cap 233 includes a conduit245 connecting that underside cavity with external service conduit 290which delivers e.g. process-sourced cooling fluid for the coupling(described previously). Pressurized fluid transported through the notedconduits fills the cavity below cap 233 and acts on stub 234 via bellow288, piston 286 and liquid provided between bellow 288 and piston 286.The sealing diameter of piston 286 is dictated by the sealing diameterof sleeve 235 and the force created by spring mechanism 239, and isspecified to ensure a substantially constant compressive axial load onsleeve 235 regardless of, e.g., pressure and temperature acting internaland external to subsea fluid system 200. For other variants of subseafluid system 200 the afore-mentioned elements are modified to ensure asubstantially constant tensile axial load is maintained on sleeve 235.Sleeve 235 may be a cylinder. The sleeve 235 may be substantially notmagnetic defining a substantially non-magnetic wall, for example, madeof a non-magnetic material. In certain instances, the sleeve 235 may bemade of an electrically conductive material that, although itexperiences an associated magnetic field, the effects of such magneticfield can be practically mitigated. The sleeve 235 may include asubstantially not conductive wall.

In certain instances sleeve 235 can be a gas-impermeable ceramic and/orglass cylinder maintained “in-compression” for all expected loadconditions by an integrated support system, e.g. external compressionsleeve 292 for radial support and stub 234-plus-sleeve support ring 270for axial support. Sleeve 235 including external compression sleeve 292are ideally made of materials and/or are constructed in such a way as tonot significantly obstruct the magnetic field of magnetic coupling 258,and to generate little if any heat from e.g. eddy currents associatedwith the coupling rotating magnetic field. In certain instances,external compression sleeve 292 can be a composite construct of highstrength fibers, such as carbon-fiber, ceramic fiber, basalt fiber,aramid fiber, glass fiber and/or another fiber in e.g. a thermoplasticor thermoset matrix. In certain instances, sleeve 235 can have metalizedend surfaces and/or other treatments to facilitate e.g. a metal-to-metalseal with the corresponding surfaces of stub 234 and sleeve support ring270.

In certain embodiments of subsea fluid system 200 electric machine 202is filled with gas, e.g. air or an inert gas such as nitrogen or argon,at or near 1-atmosphere pressure. Other than vacuum, which is difficultto establish and maintain, and which provides poor heat transferproperties, a very low gas pressure environment provides the bestconditions for operating an electric machine efficiently (e.g. low dragloss, etc.), assuming heat produced by the machine can be removedefficiently.

When submerged in deep water the pressure outside gas-filled electricmachine 202 will collapse e.g. electric machine housing 210 if it is notadequately strong or internally supported. In certain embodiments ofsubsea fluid system 200 electric machine housing 210 is thin andpossibly “finned” to improve transfer of heat between electric machine202 and the surrounding environment. Machine housing 210 may be tightlyfit around stator core 222 and sleeves 296, 298, and its ends similarlymay be tightly-fit over support surfaces provided on end-bells 214 a,214 b. The structures supporting machine housing 210 are sized to besufficiently strong for that purpose, and where practical (e.g. forsleeves 296, 298) those structures can be made using materials with auseful balance of strength-to-mass and heat-transfer properties (e.g.carbon steel, low alloy steel and select stainless steels, including 316stainless steel, and high-copper-content materials, includingberyllium-copper, respectively, among others).

FIG. 2B is a side cross-sectional view of a fluid inlet portion and themagnetic coupling 258 between an electric machine rotor 220 and afluid-end rotor 206 in an example fluid system 200 of FIG. 2A. Permanentmagnets 236 a, 236 b are affixed to an inner diameter of electricmachine rotor shaft 221 and an outer diameter of the upper end 207 ofprocess fluid rotor 206, respectively. Magnets 236 a, 236 b are unitizedto their respective rotors by sleeves 237 a, 237 b, and those sleevesserve also to isolate the magnets from their respective surroundingenvironments. Sleeves 237 a, 237 b are ideally made of materials and/orare constructed in such a way as to not significantly obstruct themagnetic field of magnetic coupling 258, and to generate little if anyheat from e.g. eddy currents associated with the coupling rotatingmagnetic field. In certain instances sleeves 237 a, 237 b can becylinders and made from an appropriate non-ferrous metal, e.g. AISI 316stainless steel or nickel chromium alloy e.g. Inconel (a product of IncoAlloys, Inc.), or they can include a composite construct of highstrength fibers such as carbon-fiber, ceramic fiber, basalt fiber,aramid fiber, glass fiber, and/or another fiber in e.g. a thermoplasticor thermoset matrix. Magnetic fields produced by permanent magnets 236a, 236 b interact across sleeve 235 to magnetically lock (for rotationalpurposes) electric machine rotor 220 and process fluid rotor 206, thusforming magnetic coupling 258.

Friction between spinning process fluid rotor 206 and fluid insidecoupling chamber 244 tends to “drag” the latter along (in the samedirection) with the former (and resists motion of the former, consumingenergy), but because friction also exists between static sleeve 235 andsaid fluid (tending to resist fluid motion), the fluid will typicallynot spin at the same speed as process fluid rotor 206. Centrifugalforces will be established in the spinning process fluid which willcause heavier elements (e.g. solids and dense liquid components) to moveoutward (toward sleeve 235) while lighter elements (e.g. less denseliquid components and gas that might have been mixed with heavierelements prior to being “spun”) will be relegated to a central core,proximate spinning process fluid rotor 206. The described relativemotion between mechanical parts and the fluid, and between differentcomponents of the fluid, among other phenomena, produces heat that islater removed from coupling chamber 244 by various mechanisms. Less heatwill be generated and less energy will be consumed by spinning processfluid rotor 206 if the fluid proximate spinning process fluid rotor 206has low density and is easily sheared, which are characteristics of gas.Fluid system 100 can supply gas into coupling chamber 244 whenever gasis available from the process stream, e.g. via stub 234 internal axialconduit 242 (and associated conduits). Regardless the properties offluid within coupling chamber 244, that (made-hot-by-shearing, etc.)fluid may be displaced with cooler fluid to avoid over-heating proximateand surrounding (e.g. motor) components.

The fluid inlet portion of FIG. 2B is located proximate electric machine202 and magnetic coupling 258. Process fluid enters fluid-end 204 bythree conduits before being combined immediately upstream of firstimpeller 241 at the all-inlets flows-mixing area 243. Because none ofthose three flows (described in greater detail below) are typicallysourced downstream of subsea fluid system 200, they have not been actedupon by subsea fluid system 200 and do not constitute a “loss” forpurposes of calculating overall system efficiency.

The majority of process fluid enters fluid-end 204 via main inlet 250.Coupling coolant enters electric machine 202 via a port 245 in cap 233,and is directed to coupling chamber 244 by conduit 242. Coolant forradial bearing 264 a enters through port 260 to join gallery 265, fromwhich it is directed through ports 251 to bearing chamber 247. For thepurpose of the current discussion, process fluid entering fluid-end 204shall be assumed to come from a common source proximate subsea fluidsystem 200 (not shown in FIG.2A), and therefore the pressure in maininlet gallery 252, coupling chamber 244 and bearing chamber 247 may beassumed to be approximately the same. The mechanism that causes fluid toenter fluid-end 204 via ports 260 and 245 with slight and “tunable”preference to main inlet 250 is the pressure drop created by inlethomogenizer 249. Pressure inside inlet flow homogenizer chamber 251, andtherefore coolant flows mixing chamber 253 (by virtue of their sharedinfluence via the all-inlets flows-mixing area 243) is lower than thesource of all inlet flows, which creates a pressure field sufficient tocreate the desired cooling flows.

For fluid in coupling chamber 244 to reach coolant flows mixing chamber253 it traverses bearing 264 a. It does so via bypass ports 269 providedin cage ring 268. For fluid in bearing chamber 247 to reach coolantflows mixing chamber 253, it first exits chamber 247 by either of tworoutes. Most fluid exits chamber 247 through the clearance gap betweenthe upper, inner bore of cage ring 268 and the outside diameter of rotorsleeve 267. Once in coupling chamber 244 it mingles with the couplingcooling fluid and reaches the coolant flows mixing chamber via bypassports 269.

Fluid may also exit bearing chamber 247 by way of seal 256 to emerge incoolant flows mixing chamber 253. An example of a seal that could beused as seal 256 is described more fully below in relation to seal 282associated with sump top plate 280. Seal 256 has a much smallerclearance relative to rotor sleeve 267 than does cage ring 268 (locatedat the top of bearing 264 a), and has a much lower leakage rate as aresult. This configuration encourages fluid entering bearing chamber 247to exit there-from at the upper end of bearing 264 a. That biasin-combination with gravity and centrifugal forces pushing heavier fluidcomponents (e.g. liquids) down and radially outward, respectively, alsocauses any gas that might be entrained in the fluid stream enteringbearing chamber 247 to move radially inward so that it is exhaustedimmediately past cage ring 268.

Keeping gas out of bearing chamber 247 and removing it quickly should itcome to be present in bearing chamber 247 will promote good performanceand long life for fluid-film bearing 264 a. To increase the likelihoodthat bearing 264 a active surfaces are constantly submerged in liquid(i.e. inside surfaces of tilt-pads 266 and outside surface of rotorsleeve 267 adjacent to tilt-pads 266), tilt-pads 266 are positioned tointeract with rotor sleeve 267 on a larger diameter than the gaps (aboveand below tilt-pads 266) that allow fluid to move out of bearing chamber247. The natural tendency for gas to separate from liquid and movetoward the center of rotation in a rotating fluid system will ensure gasmoves out of bearing chamber 247 in advance of liquids whenever gas ispresent within bearing chamber 247. Adding an additional seal 256 thatis positioned above the bearing chamber 247 can improve the ability tomanage the gas inherently present in the process stream.

In some embodiments of subsea fluid system 200, process fluid combinedimmediately upstream of first impeller 241 at the all-inletsflows-mixing area 243 is downstream-thereof increased in pressure byhydraulic stages including impellers secured to process fluid rotor 206interacting with interspersed static diffusers (a.k.a. stators). Staticand dynamic seals are provided at appropriate locations within thehydraulic stages to minimize back-flow from higher-to-lower pressureregions, thereby improving the hydraulic performance of fluid-end 204.

FIG. 2C is a side cross-sectional view of a fluid outlet portion andsump of an example fluid-end 204 of FIG. 2A. There are five main regionsof interest in this area separated by two significant functionalelements. Those elements are process fluid rotor thrust balance device259 and sump top plate 280. Above, surrounding and below thrust balancedevice 259 are final-stage impeller 255, fluid-end 204 outlet gallery257, and balance circuit outlet device 261 (shown in FIG. 2C asintegrated with sump top plate 280, which is not a strict requirement),respectively. Above and below sump top plate 280 are balance circuitoutlet device 261 and sump 271, respectively.

The highest pressure in certain embodiments of subsea fluid system 200may occur immediately downstream of final-stage impeller 255. By passingthrough openings 278 provided in balance device stator 263, processfluid enters outlet gallery 257 at a slightly lower pressure, and exitsinto process fluid outlet 272 which is connected to a downstream pipesystem. Total pressure change from final-stage impeller 255 to the pointof entry to the downstream pipe may be a reduction (small, if e.g. careis taken in design of balance device stator 263 fluid paths 278, volutegeometry is provided in outlet gallery 257, and the transition fromoutlet gallery 257 is carefully contoured, etc.) or an increase (forsome embodiments with some fluids for a well-executed volute).

When submersible fluid system 200 is not operating, i.e. when processfluid rotor 206 is not spinning, fluid entering fluid-end housing 208 atinlet 250 and flowing past the hydraulics stages (impellers/diffusers)to exit through outlet 272 will impart relatively little axial force onprocess fluid rotor 206. When process fluid rotor 206 is spinning, theinteraction of the impellers, diffusers and associated componentscreates pressure fields that vary in magnitude depending on local fluidproperties existing at many physical locations within fluid-end 204.Those multiple-magnitude pressure fields act on various geometric areasof process fluid rotor 206 to produce substantial thrust. Such thrustgenerally tends to drive process fluid rotor 206 in the direction ofinlet 250, however various operating scenarios may produce “reversethrust”. Depending on thrust magnitude and direction, thrust bearing 291may possess sufficient capacity to constrain process fluid rotor 206. Inthe event thrust acting on process fluid rotor 206 exceeds the capacityof a practical thrust bearing 291, considering the many complextradeoffs known to those skilled in the art of fluid-ends design, athrust balance device 259 may be used. Thrust bearing 291 is locatednear the lower end of fluid-end housing 204. Thrust bearing 291 includesan upward-facing bearing surfaces on thrust collar 294 (coupled to fluidrotor 206), and downward-facing bearing surfaces on the fluid-endhousing 208, the bearing surfaces cooperate to support the upward thrustof the fluid rotor 206. Similar components and associated surfaces areprovided on the opposite side of thrust collar 294 to resist “reversethrust” and other scenarios causing fluid rotor 206 to tend to movedownward.

Various types of thrust balance devices are known, with the two mostcommon being referred to as “disk” and “piston” (or “drum”) types. Eachtype of device has positive and negative attributes, and sometimes acombination of the two and/or a different device altogether isappropriate for a given application. Embodiments described hereininclude a piston-type thrust balance device; however, other types may beimplemented.

A piston-type thrust balance device is essentially acarefully-defined-diameter radial-clearance rotating seal createdbetween process fluid rotor 206 and a corresponding interface togenerate a desired pressure-drop by exploiting pressure fields alreadyexisting in fluid-end 204 to substantially balance the thrust loadsacting on process fluid rotor 206. The thrust balance device includestwo main components (not including process fluid rotor 206), however afluid conduit (balance circuit conduit 276) connecting the lowpressure-side of thrust balance device 259 to inlet 250 pressure is alsoprovided. Balance device rotor 265 is secured to process fluid rotor 206in a way that provides a pressure-tight seal there-between. As analternative, the profile of balance device rotor 265 may be provided asan integral part of fluid rotor 206. Balance device stator 263 issecured to fluid-end housing 208 via sealed interfaces with othercomponents. A small clearance gap is provided between balance devicerotor 265 and stator 263 to establish a “rotating seal.” High pressurefrom final-stage impeller 255 acts on one side of balance device rotor265 while low pressure corresponding to that in inlet 250 acts on theother side. Inlet 250 pressure is maintained on the low pressure side ofbalance device 259 despite high pressure-to-low pressure fluid leakageacross the clearance gap (between the balance device rotor 265 andstator 263) because such leakage is small compared to the volume offluid that can be accommodated by balance circuit conduit 276. Balancecircuit outlet device 261 collects and redirects fluid exiting balancedevice 259 to deliver it to balance circuit conduit 276. The nominaldiameter of the clearance gap (which defines the geometric areas onwhich relevant pressures act) is selected to achieve the desired degreeof residual thrust that must be carried by thrust bearing 291 (note thatsome residual is valuable from bearing loading and rotor dynamicstability perspectives).

Returning briefly to thrust bearing 291, the side that is normallyloaded in operation is referred to as the “active” side (upper side inFIG. 2C), whereas the other side is referred to as the “inactive” side.In certain embodiments, the active side of thrust bearing 291 isprotected during high-risk long-term storage, shipping, transportation,and deployment activities by maintaining it “un-loaded” during suchactivities. Specifically, process fluid rotor 206 “rests” on inactiveside of thrust bearing 291 whenever subsea fluid system 200 is notoperating, e.g. during storage, handling, shipping and deployment. Thisarrangement is advantageous because design attributes that increasetolerance to e.g. high impact loads during deployment, which howevermight reduce normal operating capacity, can be implemented for theinactive side of thrust bearing 291 without affecting the operatingthrust capacity of fluid-end 204. Such design attributes (among others)may include selection of bearing pad materials that are tolerant ofprolonged static loads and/or impact loads, and that however do not havehighest-available operating capacity. In addition, one or more energyabsorbing devices 295 e.g. dampers, springs, compliant pads (made ofelastomeric and/or thermoplastic materials, etc.) and/or “crushable”devices (ref “crumple zones” in automobiles) may be added integral toand/or below thrust bearing 291, as well as external to fluid-endhousing 208 (including on skid 110 and/or on shipping stands, runningtools, etc.—see damper 120 described in FIG. 1). It may also beadvantageous to “lock” rotors 206, 220 so that they are prevented from“bouncing around” during e.g. transportation, deployment, etc., or tosupport them on “stand-off” devices that prevent e.g. critical bearingsurfaces from making contact during such events. Such locking andstand-off functionality may be effected using devices that may bemanually engaged and/or released (e.g. locking screws, etc.), orpreferably devices that are automatically engaged/disengaged dependingon whether rotors 206, 220 are stopped, spinning, transitioning-to-stopor transitioning-to-spin. Devices providing aforementioned attributesinclude permanent magnet and/or electro-magnet attraction devices, amongothers (“locking” devices), and bearing-like bushings orpad/pedestal-like supports, among others, that present geometry suitableto the stand-off function while rotors 206, 220 are not spinning andpresent e.g. “less intrusive” geometry that permits the bearings(intended to support rotors 206, 220 during operation) to effect theirfunction when rotors 206, 220 are spinning (“stand-off” devices).Displacement mechanisms that might enable the “dual-geometry” capabilitydesired for “stand-off” devices include mechanical, hydraulic, thermal,electric, electro-magnetic, and piezo-electric, among others. Passiveautomatic means for enacting the locking and/or stand-off functions maybe used, however a control system may also be provided to ensure correctoperation.

Sump top plate 280 in combination with seals 282 and 273 substantiallyisolate fluid in sump 271 from interacting with fluid-end 204 processfluid. Sump 271 contains fluid-film type radial bearing 264 b and thrustbearing 291. To enable good performance and long service life,fluid-film bearings are lubricated and cooled with clean liquid, andprocess fluid (especially raw hydrocarbon process fluid) may containlarge volumes of gas and/or solids that could harm such bearings.

Seal 282 may be substantially the same as seal 256 associated with upperradial bearing 264 a described previously. Seal 282 is secured to sumptop plate 280 and effects a hydrodynamic fluid-film seal (typicallymicro-meter-range clearance) relative to rotor sleeve 275 (shown in FIG.2C as integrated with bearing sleeve 288, which is not a strictrequirement) when process fluid rotor 206 is spinning, and also a staticseal (typically zero-clearance) when process fluid rotor 206 is notspinning In certain instances, the seal 282 can include a plurality ofpads springingly biased inward against the rotor shaft to provide thestatic seal, but enable formation of the hydrodynamic fluid-film sealwhen the rotor is rotating. Seal 282 may be designed to maintain,increase or decrease its hydrodynamic clearance, even to zero clearancein operation, when subjected to differential pressure transients fromeither side (above or below), and therefore to substantially maintain,increase or decrease, respectively, its leakage rate during especiallysudden pressure transients. Seal 282 includes features enabling itshydrodynamic performance that allow a small amount of leakage in dynamic(regardless the clearance magnitude relative to rotor sleeve 275) andstatic modes whenever it is exposed to differential pressure, andtherefore it may for some applications be characterized as aflow-restrictor instead of an absolute seal. A small amount of leakageis desired for the sump 271 application. The seals 273 and 282 sealbetween the fluid-end housing 208 and the fluid rotor 206, and define anupper boundary of a sump 271 of the fluid-end housing 208. A fluidbearing 291 resides in the sump 271 and the seal 282 is responsive toprovide a greater seal when subjected to a change in pressuredifferential between the sump and another portion of the fluid-endhousing.

Prior to deployment, and using port(s) 277 provided for such purpose (aswell as for refilling sump and/or flushing sump of gas and/or debris,etc.), sump 271 may be filled with a fluid ideally having attractiveproperties for the target field application, e.g. chemically compatiblewith process fluid and chemicals that might be introduced into processstream and/or sump 271, density greater than process fluid, usefulviscosity over wide temperature range, good heat-transfer performance,low gas-absorption tendency, etc. Following installation and uponcommissioning (during which time subsea fluid system 200 is operated),fluid-end 204 will be pressurized in accordance with its design and sump271 temperature will rise significantly, the latter causing sump fluidto expand. The ability of Seal 282 to transfer fluid axially in bothdirections ensures pressure in sump 271 will not rise significantly as aresult, and further ensures that pressure in sump 271 will substantiallymatch fluid-end 204 inlet 250 pressure during operating andnon-operating states, except during process fluid rotor 206 axialposition transients (explained below).

The low-leakage-rate, static sealing and hydrodynamic sealingcapabilities of seal 282, combined with an otherwise “sealed” sump 271,provide unique and valuable attributes to fluid-end 204. Seal 282provides a low leakage rate even when subject to suddenhigh-differential pressure, and therefore equalizes pressure more orless gradually depending mainly on the initial pressure differential andproperties of fluid involved (e.g. liquid, gas, multiphase, high/lowviscosity, etc.). In one scenario, prior to starting to spin processfluid rotor 206, an operator may inject liquid into port 277 at a ratesufficient to create a pressure differential across seal 282 adequate toelevate process fluid rotor 206, thereby avoiding a potential rotordynamic instability that might accompany transitioning from the“inactive” side of thrust bearing 291 (not normally used) to the“active” side (used during normal operations) upon start-up. In anotherscenario, almost the reverse process may be employed. That is, prior tostopping rotation of process fluid rotor 206, liquid may be injectedinto port 277 at a rate sufficient to maintain elevation thereof. Uponshut-down, process fluid rotor 206 will continue to be elevated until ithas ceased to spin, at which point liquid injection through port 277 canbe halted to allow process fluid rotor 206 to land softly, withoutrotation, onto the inactive surfaces of thrust bearing 291. That willreduce damage potential and thereby promote long bearing life. Inanother scenario, any tendency to drive process fluid rotor 206 intosump 271 (“reverse thrust”) will encounter “damped resistance” owing tothe fact fluid must typically bypass seal 282 (which happens onlyslowly) in order for process fluid rotor 206 to move axially. Similarresistance will be encountered if process fluid rotor 206 is motivatedto rise quickly from its fully-down position, however fluid must passseal 282 to enter sump 271 in that case. The foregoing “damped-axialtranslation” attribute will protect thrust bearing 291 and therebypromote long-life for submersed fluid system 200. In another scenario,in the event process gas permeates sump fluid, and inlet 250 (whichdictates sump nominal pressure) is subsequently subject to a suddenpressure drop, seal 282 will only gradually equalize sump pressure tothe lower inlet 250 pressure and thereby prevent a sudden expansion ofsump gas that might otherwise evacuate the sump. This is a scenario forwhich designing seal 282 to “reduce its clearance relative to rotorsleeve 275 when subject to differential pressure transients” (describedpreviously) may be applicable. As noted previously, maintaining liquidin sump 271 will facilitate the health of bearings 264 b, 291. In anyscenario that potentially subjects spinning process fluid rotor 206 to“reverse thrust,” pressure higher than at-that-time-present in inlet 250(and therefore sump 271) may be applied to sump port 277 to resist such“reverse-thrust” and thereby protect e.g. the inactive-side elements ofthrust bearing 291. A substantial sensor suite and associatedfast-acting control system, possibly including automation algorithms,actuated valves and high pressure fluid source may be used to effect the“process fluid rotor active shaft thrust management” functionalityherein described. It shall be understood that similar ability to applypressure to the top of process fluid rotor 206 (e.g. via supplementaryfluid conduit 308 and gas conduit 321 discussed later in thisdisclosure) may be developed to provide sophisticated “active thrustmanagement” for fluid-end 204.

Significant heat will be generated in sump 271 caused by fluid-shear andother phenomena associated with spinning process fluid rotor 206 andattached thrust collar 294. Cooling sump fluid to optimize itsproperties for maintenance of bearing performance is achieved bycirculating the fluid through a heat exchanger 301 positioned in watersurrounding fluid-end 204. Careful positioning of flow paths in andaround bearings 264 b, 291, and for heat exchanger 301 inlet and outletports (302 and 300, respectively), combined with naturally occurringconvection currents and aided by e.g. volute-like and/or flow-directing(e.g. circumferential-to-axial) geometry in sump lower cavity 285, willcreate a “pumping effect” for sump 271. Such pumping effect can beenhanced by adding features, e.g. “scallops”, “helixes”, “vanes”, etc.,to the outside of rotating elements including process fluid rotor 206(e.g. at locations 279, 281; latter on the end-face and/or possibly onan extension of process fluid rotor 206) and/or thrust collar 294 (e.g.at location 283). Alternatively or in addition, an impeller or similardevice may be attached to the lower end of process fluid rotor 206.

It is unlikely that process fluid-borne solids of significant size orvolume will make their way into sump 271 of fluid system 200. As notedpreviously, sump 271 is normally pressure-balanced with respect to inlet250 via balance circuit conduit 276, so there is normally no fluid flowbetween sump 271 and fluid-end 204 process fluid-containing areas.Additionally, seal 282 allows only small-volume and low-rate fluidtransfer there-across (even during high differential pressuretransients). Furthermore, a convoluted path with multiple interspersedaxial and radial surfaces exists between the underside of balance devicerotor retainer 298 and the top of sump top-plate 280, so solids mustintermittently move upward against gravity and inward against thecentrifugal force before they can approach the top of seal 282.Regardless, two or more ports 277 may be provided to circulate liquidthrough sump 271 and/or heat exchanger 301 to effectively flush same, atleast one port for supplying fluid and one for evacuating fluid (e.g. toany conduit or vessel located upstream of inlet 250 or downstream ofoutlet 272). Ports 277 may be provided to intersect sump lower cavity285 (as shown in FIG. 2C), which represents a large diameter and thelowest point in sump 271, and also an area where solids are likely tocollect. Alternative locations for ports 277 may also be provided, andmay provide additional benefits including an ability to deliverhigh-rate flow of liquids directly into heat exchanger 301 to flushsolids and/or gas (should either of the latter become trapped therein).Note that heat exchanger 301 may take many forms in addition to thatshown in FIG. 2C, including some optimized for solids removal and/or gasremoval.

FIG. 3 illustrates an example subsea fluid system 300 that might bepackaged within fluid system 100 of FIG. 1 for the purpose of extractingdiscrete service-fluid streams from a multiphase process stream to servethe needs of specific elements within subsea fluid system 300 (also200). Subsea fluid system 300 contains an integrated electric machine301, fluid-end 302 and magnetic coupling 303 as described previously forsubsea fluid system 200 of FIGS. 2A-C. It also contains upstream anddownstream processing packages 304 and 305, respectively. Upstreamprocessing package 304 includes a buffer tank 306, a liquid reservoir307, a supplementary fluid conduit 308 and a selection of flow controldevices and interconnecting pipe-work, of which various elements will bedescribed later in this disclosure. Downstream processing package 305contains a liquid extraction unit 339 and a flow regulating device(a.k.a. choke or process control valve) 309. An optional downstreamservice conduit 336 including isolation valve 337 may be provided toconnect liquid extraction unit 339 with e.g. liquid conduit 330 (forreasons explained below).

Multiphase fluid enters subsea fluid system 300 at inlet 310 fortransport through inlet pipe 311 to buffer tank 306. Raw hydrocarbonproduction fluids delivered to subsea fluid system 300 from wells,directly or by way of e.g. manifolds, may at various times include asmuch as 100% gas or 100% liquids, as well as all fractional combinationsof gas and liquids (often with some volume of solids in addition).Transition between gas-dominated and liquid-dominated multiphase streamsmay occur frequently (e.g. time frame of seconds or less) or rarely, andsuch transitions may be gradual or abrupt. Abrupt changes from very highGas Volume Fraction (GVF) streams to very low GVF streams, andvice-versa (typically referred to as “slugging”), can be harmful tosubmersed fluid system 300 for reasons known to those skilled in the artof fluid-boosting devices and associated pipe systems. Buffer tank 306can accommodate even rapidly changing fluid conditions at inlet 319 andreduce the abruptness of such fluid condition changes at its main outlet320, and in so doing moderate the detrimental effects on downstreamfluid system 300. Buffer tank 306 amounts to a “fat spot” in inlet pipe311 that allows fluid to reside there long enough for gravity to driveheavier streams/elements (liquid, solids) to the bottom of the tankwhile simultaneously forcing gas to rise to the top of the tank. Aperforated stand-pipe 312 or similar device controls the rate at whichthe separated streams/elements are rejoined before exiting the tank atmain outlet 320. Notably, when a high-GVF multiphase flow stream entersbuffer tank 306 the volume of gas in the tank may increase relative tothe volume of liquid/solids already in the tank, and similarly when alow-GVF stream enters the tank the opposite may occur. Meanwhile, theGVF of the fluid exiting the tank will typically be different from thatentering because the exit-stream GVF is automatically (and gradually)adjusted in accordance with the volume of gas and liquid/solidspermitted to enter perforated stand-pipe 312. The gas/liquid interfacelevel in buffer tank 306 dictates the flow area (number of holes)accessible to each stream.

In certain embodiments of subsea fluid system 300, separated gas 313 andseparated liquid 314 may be extracted from buffer tank 306 throughgas-tap 315 and liquid-tap 316, respectively. It is beneficial that nosolids enter conduits downstream of gas-tap 315 and liquid tap 316.Solids in the fluid stream entering buffer tank 306 will typically becarried there-through with the liquid phase(s), therefore, while somescenarios may be envisioned for which solids may enter gas-tap 315(typically accompanied by liquids) or be formed in gas conduit 321,subsea fluid system 300 is operated to minimize the chance for thosescenarios occurring. The large size of liquid-tap 316 relative to thesmall size of, and flow rate in, conduits downstream thereof enables asubstantially quiescent environment to establish within liquid-tap 316that allows solids to settle-out therein. The steep angle of liquid-tap316 suggested in FIG. 3 promotes gravity-driven return of settled-solidsto the main chamber of buffer tank 306, from which they can subsequentlyexit through main outlet 320. Baffle(s) 317 and/or similar device(s)and/or features may be added to liquid-tap 316 to enhance thesolids-separation effect and/or otherwise inhibit transfer of solids toareas downstream of liquid-tap 316.

Downstream of liquid-tap 316 is normally-open valve 318 through whichideally only liquid will pass to enter liquid reservoir 307. Levelmonitor 327 provides the sensory feedback needed for an associatedcontrol system to command valve 318 to close if buffer tank 306 liquidlevel gets close to liquid-tap 316 level and threatens to permit anunacceptable volume of gas to enter liquid reservoir 307 by that route.Liquid reservoir 307 and the conduit including valve 318 may bevertically oriented, and they are attached to liquid-tap 316 in such away that solids possibly remaining in fluid delivered to those spacesmay settle and drop into liquid-tap 316 (and subsequently, buffer tank306) so as not to be carried downstream of liquid reservoir 307. Fluidin liquid reservoir 307 will typically be quite still and under certaincircumstances reside therein for several minutes before the liquid phasemakes its way further downstream, substantially free of solids andfree-gas.

There are two other flow paths into/out-of liquid reservoir 307,specifically gas conduit-link 322 with normally-open isolation valve 323and liquid conduit-link 324 with normally-open isolation valve 325. Itis beneficial that only gas flows through gas conduit-link 322, and thatonly liquid flows through liquid conduit-link 324. Level monitor 329provides the sensory feedback needed for an associated control system tocommand valve 325 to close if liquid reservoir 307 liquid level getsclose to liquid conduit-link 324 level and threatens to permit free-gasto enter there-into. The main scenario for which valve 323 might beclosed is related to flushing of solids from liquid reservoir 307, whichis described elsewhere in this disclosure.

Liquid reservoir 307 liquid level may be forced higher in an absolutesense than that in buffer tank 306 by manipulating isolation valves 323,325 and gas flow-control device (a.k.a. choke or process control valve)326. Maintaining liquid reservoir 307 substantially full of liquid isnecessary for optimum performance. Using choke 326 to reduce pressure ingas conduit 321 relative to pressure in buffer tank 306 (therefore alsoin liquid tap 316 and liquid reservoir 307) will cause fluid in liquidreservoir 307 to flow toward (into) gas conduit 321. Gas in liquidreservoir 307, whether introduced through liquid tap 316 (as free-gas orgas-in-solution) or gas conduit-link 322, will naturally collect nearthe top of liquid reservoir 307 and therefore be exhausted into gasconduit 321 before liquids entering from below during the “liquidreservoir filling” process. Level monitor 329 provides the sensoryfeedback needed to effect a level-control system for liquid reservoir307.

Liquid reservoir 307 is provided to hold a volume of liquid sufficientto lubricate bearing 264 a (referred to with respect to the descriptionof FIG. 3, but shown in FIG. 2B) for a specific period of time in theevent liquid ceases to be available from buffer tank 306 for such periodof time. The period of time depends on several factors of which liquidreservoir 307 size, pressure drop across fluid-end inlet homogenizer249, leakage rate from bearing chamber 247, rate of fluid exitingcoupling chamber 244 via bypass ports 269, and liquid viscosity aresome. Knowing the flow behavior and physical properties of processfluids entering inlet 310 allows for correctly sizing liquid reservoir307. Recognizing it is difficult to predict such attributes for newproducing fields, and to predict how such attributes may vary over themany years most fields are expected to produce, in-field replacement ofliquid reservoir 307 with e.g. a larger unit, independent of otherelements within submersible fluid system 300, 100 and/or in-combinationwith other elements within submersible fluid system 300, 100, may beenabled. While specific in-field-replacement-enabling features forliquid reservoir 307 are not described in detail in this disclosure(FIG.1 shows process connectors 115 suggesting how such capability mayalso be provided for fluid system 100 containing liquid reservoir 307),it shall be obvious to one skilled in the art of designing modular,replaceable submersible systems how such capability may be effected.

Nozzle 328 is the inlet to liquid conduit-link 324, and it may also beused as an outlet device for a function described later in thisdisclosure. It may be configured in any number of ways and/or associatedwith devices e.g. baffles and/or deflectors to passively resist intakeof solids that might remain in liquid entering or stored in liquidreservoir 307. Typically one or more substantially side-directed ordownward-directed ports may be used instead of a port or ports angledupward to avoid the undesirable tendency of the latter alternatives tocollect solids that might settle-out of liquid reservoir 307 fluids,then transfer such solids to elements downstream thereof. One or more ofany number of filtering features and/or devices may also be provided toresist intake of solids, regardless the orientation of the noted ports.

Unless forced to behave otherwise by e.g. a flow restriction and/oradded flow-boosting device, fluid (e.g. liquid) will exit liquidreservoir 307 to flow through liquid conduit 330 into bearing 264 a at arate dictated at least by pressure drop across fluid-end inlethomogenizer 249, leakage rate from bearing chamber 247, rate of fluidexiting coupling chamber 244 via bypass ports 269, and liquid viscosity.Isolation valves 331, 332, 333 associated with supplementary fluidconduit 308 are normally closed, and therefore do not normally affectflow rate through liquid conduit 330 (or gas conduit 321). Normally-openisolation valve 334, when closed or substantially closed, enables fluidsupplied from a source capable of delivering fluid at pressure greaterthan that in buffer tank 306, such as supplementary fluid conduit 308 ordownstream service conduit 336 (when accessed by opening normally-closedisolation valve 337), to be directed into liquid reservoir 307 vianozzle 328 to e.g. fill liquid reservoir 307 with liquid and/or to flushsolids out of liquid reservoir 307 (past valve 318 into liquid-tap 316and into buffer tank 306). If it is desired to increase pressure inliquid conduit 324 upstream of closed or substantially closed isolationvalve 334 to e.g. create or intensify a “jetting action” produced bye.g. nozzle 328, a pump 335 may be added (typically not required fordownstream service conduit 336, however possibly useful forsupplementary fluid conduit 308). An alternative to isolation valve 334is a choke or a process control valve, which is generally better able toaccommodate partial opening and associated potentially large pressuredrop without suffering significant wear. Such alternative choke orprocess control valve, when associated with suitable instrumentatione.g., upstream, downstream and/or differential pressure sensors, andcontrol algorithms (controller) facilitates increased controllability ofliquid flow provided to bearing 264 a, and therefore the rate ofconsumption of liquid in liquid reservoir 307.

A sufficiently sophisticated control system possibly includingautomation algorithms will be able to operate the various valves andespecially chokes/process control valves (326 and that which is analternative to isolation valve 334) to optimize coolant flows forbearing 264 a and magnetic coupling 258, and possibly to effect “activethrust management” for fluid-end rotor 206. The controller may beconfigured to receive gas and liquid pressure information and e.g.component position information, etc., from one or more sensors locatedat relevant points within submersible fluid system 200 and furtherconfigured to control one or more pressure regulating devices to adjustgas or liquid pressures in the submersible fluid system. In someapplications the cost to obtain the flexibility and performanceenhancement delivered by an instrumented choke, process control valve orother variable-position valve (an option for isolation valve 334) is notjustified, and a fixed flow restriction (e.g. orifice or venturi) or noflow restriction may be adequate to ensure an acceptable supply ofliquid is delivered to bearing 264 a. Regardless, at least anopen/close-type isolation valve 334 may be used to enable direction offluids in the manner and for the same purpose described below forisolation valve 338.

Normally-open isolation valve 338 is provided in gas conduit 321 so thatit may be closed on select specific occasions, e.g. following shut-downof submersible fluid system 200 when the duration of such shut-down isexpected to be sufficiently long that process fluids may undergoproperty changes that might be detrimental to subsequent operation offluid system 300 (and 200). With isolation valve 338 closed, chemicalssupplied by supplementary fluid conduit 308 can be routed selectively toalternative locations throughout submersible fluid system 300 todisplace potentially undesirable process fluids and/or to otherwiseprotect against undesirable consequences, e.g. formation of hydrates,wax, etc. Note that the ability to provide heat to critical locationswithin submersible fluid systems described herein may be desirable, andmay be accomplished using known techniques e.g. electric heat-tracingand/or heated fluids circulated through dedicated conduits, etc.

Several functions have been described already for supplementary fluidconduit 308. Another function is to provide liquid to bearing 264 a foras long as necessary in the event liquid becomes unavailable on acontinuous basis from buffer tank 306 and for an additional period oftime from liquid reservoir 307 (e.g. limited by its size). Thefacilities supplying supplementary fluid conduit 308, e.g. topsidehydraulic power unit (HPU) and associated electric power supply, plus asingle or multi-conduit umbilical to transport the chemicals from theHPU to proximate the underwater points of use, are provided for subseaproduction systems as a matter of course to provide mitigation ofpotential “flow assurance” issues such as those mentioned throughoutthis disclosure (e.g. hydrates, wax, scale, etc.).Multiphase-process-fluid-capable submersible fluid systems describedherein do not require that an additional topside HPU, electric powersupply, umbilical conduits, and other expensive equipment (known as a“barrier fluid system”) be provided to cool and lubricate their bearingsand other sensitive components.

Fluid systems disclosed herein are sophisticated devices designed toperform complex and challenging functions reliably over extended periodsof time. They contain many active devices including electric machines,fluid-ends, auxiliary pumps, valves and sensing instruments, amongothers. Condition and Performance Monitoring (CPM) of such devices andsub-systems is recommended, and that requires that equally sophisticateddata collection, reduction, historian, control and potentiallyautomation systems be implemented.

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made. Accordingly, otherembodiments are within the scope of the following claims.

What is claimed is:
 1. A submersible fluid system for operatingsubmersed in a body of water, the system comprising: a fluid-endcomprising a fluid rotor disposed in a fluid-end housing; an electricmachine housing coupled to the fluid-end housing and comprising ahermetically sealed cavity; an electric machine disposed entirely withinthe hermetically sealed cavity of the electric machine housing, theelectric machine comprising an electric machine stator and an electricmachine rotor; and a magnetic coupling that couples the electric machinerotor and the fluid rotor, the magnetic coupling comprising a magnetwithin the hermetically sealed cavity of the electric machine housing,the magnet coupled to the electric machine rotor; wherein thehermetically sealed cavity of the electric machine housing contains agas at a pressure that is less than a pressure of a fluid entering thefluid rotor of the fluid-end and less than a hydrostatic pressure of afluid surrounding the electric machine housing when submerged at aspecified depth.
 2. The system of claim 1, wherein the magnetic couplingfurther comprises: a magnet coupled to the fluid rotor and in magneticinteraction with the magnet of the electric machine rotor.
 3. The systemof claim 1, further comprising a substantially non-magneticallyconductive wall between a magnet of the electric machine rotor side ofthe magnetic coupling and a magnet of the fluid rotor side of themagnetic coupling.
 4. The system of claim 3, wherein: a drive-end of thefluid rotor extends into an interior bore of the electric machine rotorand the magnet of the fluid rotor is coupled to an exterior of thedrive-end; the magnet of the electric machine rotor resides in theinterior bore of the electric machine rotor; and the wall comprising asubstantially non-magnetically conductive cylinder is disposed withinthe interior bore of the electric machine rotor.
 5. The system of claim4, wherein the cylinder comprises at least one of a gas impermeableceramic or glass inner sleeve within a fiber-matrix composite outersleeve.
 6. The system of claim 5, wherein the outer sleeve compressivelystrains the inner sleeve.
 7. The system of claim 4, wherein the cylindercomprises at least one of gas impermeable ceramic or glass inner sleevewithin a fiber-matrix composite outer sleeve, and at least one of theinner or outer sleeves comprises a seal surface about one end and a sealsurface about an opposite end.
 8. The system of claim 4, wherein thehermetically sealed cavity of the electric machine housing contains agas at a pressure of at or near 1-atmosphere and an interior of thecylinder contains a fluid at a pressure at or near the pressure of fluidentering the fluid rotor of the fluid-end.
 9. The system of claim 1,wherein the electric machine comprises a magnetic bearing supporting theelectric machine rotor to rotate within the electric machine stator, andthe bearing is wholly contained within the hermetically sealed cavity.10. The system of claim 1, further comprising a plurality of sealssealing the hermetically sealed cavity, and wherein the seals areentirely static seals.
 11. The system of claim 10, wherein at least oneof the seals comprises a metal-to-metal seal.
 12. The system of claim 1,wherein the electric machine rotor comprises a permanent magnet thatinteracts with the stator to at least one of rotate the electric machinerotor relative to the stator or generate electricity when moved relativeto the stator.
 13. The system of claim 1, wherein the electric machinecomprises a motor and the fluid rotor comprises one or more of a pumprotor or a compressor.
 14. The system of claim 1, wherein the electricmachine comprises a generator.
 15. A submersible fluid system foroperating submersed in a body of water, the system comprising: afluid-end comprising a fluid rotor disposed in a fluid-end housing; anelectric machine housing coupled to the fluid-end housing and comprisinga hermetically sealed cavity; an electric machine disposed entirelywithin the hermetically sealed cavity of the electric machine housing,the electric machine comprising an electric machine stator and anelectric machine rotor; and a magnetic coupling that couples theelectric machine rotor and the fluid rotor; further comprising asubstantially non-magnetically conductive wall between a magnet of theelectric machine rotor side of the magnetic coupling and a magnet of thefluid rotor side of the magnetic coupling; a drive-end of the fluidrotor extends into an interior bore of the electric machine rotor andthe magnet of the fluid rotor is coupled to an exterior of thedrive-end; the magnet of the electric machine rotor resides in theinterior bore of the electric machine rotor; the wall comprising asubstantially non-magnetically conductive cylinder is disposed withinthe interior bore of the electric machine rotor; and further comprisinga support extending from an end of the electric machine housing towardthe fluid-end housing and clamping to axially strain the substantiallynon-magnetically conductive cylinder between the support and thefluid-end housing.
 16. The system of claim 15, wherein the support isspring biased toward the fluid-end housing.
 17. The system of claim 15,further comprising a fluid passage through the support and into aninterior of the substantially non-magnetically conductive cylinder, thefluid passage coupled to receive fluid from an exterior of the systemand communicate the fluid to an interior of the cylinder.
 18. The systemof claim 17, wherein the fluid comprises substantially gas.
 19. A methodof coupling an electric machine to a fluid-end in a submersible fluidsystem, the method comprising: maintaining a rotor of the electricmachine in an area of a first pressure in a hermetically sealed cavitydefined by an electric machine housing, the rotor hermetically sealedfrom a fluid rotor of the fluid-end in an area of a second, differentpressure, the rotor comprising a rotor permanent magnet in thehermetically sealed cavity defined by the electric machine housing; andcoupling the rotor of the electric machine to the fluid rotor with amagnetic coupling through a stationary wall between the rotor of theelectric machine and the fluid rotor; wherein the first pressure is lessthan the second pressure, and the first pressure is less than ahydrostatic pressure of a fluid surrounding the electric machine housingwhen submerged at a specified depth.
 20. The method of claim 19,comprising sealing the area containing the rotor of the electric machinefrom the area containing the fluid rotor entirely with static seals. 21.The method of claim 20, comprising maintaining a stator of the electricmachine in the area of the first pressure.
 22. A fluid system,comprising: a pump shaft contained in a submersible pump housing, thepump shaft having a pump permanent magnet; a rotor extending from an endof an electric machine housing, the rotor having a rotor permanentmagnet and residing in a hermetically sealed cavity defined by theelectric machine housing; and the pump permanent magnet residingproximate to the rotor permanent magnet communicating magnetic fluxbetween the rotor permanent magnet and the pump permanent magnet andcoupling the pump shaft with the rotor; wherein the hermetically sealedcavity of the electric machine housing contains a gas at a pressure thatis less than a pressure of a fluid entering the fluid rotor of thefluid-end and less than a hydrostatic pressure of a fluid surroundingthe electric machine housing when submerged at a specified depth. 23.The fluid system of claim 22, wherein the rotor is configured to rotatewithin a stator, and the magnetic coupling couples the rotor to the pumpshaft to rotate the pump shaft at the same speed as the rotor.